Abstract: Recurrent spontaneous abortion is that a patient suffered from spontaneous abortion for three times or more than three times continuously with the same man. Appropriate complement inhibition is an absolute requirement for normal pregnancy. Uncontrolled complement activation in the maternal-fetal interface leads to fetal death and recurrent spontaneous abortion including other pregnancy complications. It is said that complement system is abnormally activated by classical pathway or alternative pathway in murine models in RSA， and C3a or C5a may lead to RSA by sFlt-1 pathway and tissue factor way. However， there is still dispute on key pathways for complement activation， indispensable complement constituent， and the effector mechanisms leading to fetal loss， which need more researches to explore.

Key words: Abortion, habitual, Complement C3, Complement C5a, Disease models, animal